To determine the number of significant figures in a number, we follow these rules: 1. All nonzero digits are significant. 1.05 0.0110 2. Interior zeros (zeros between two numbers) are significant. 4.0208 50.1 3. Trailing zeros (zeros to the right of a nonzero number) that fall after a decimal point are significant. 5.10 3.00 4. Trailing zeros that fall before a decimal point are significant. 50.00 1700.24 5. Leading zeros (zeros to the left of the first nonzero number) are not significant. They only serve to locate the decimal point. o For example, the number 0.0005 has only one significant digit. 6. Trailing zeros at the end of a number, but before an implied decimal point, are ambiguous and should be avoided by using scientific notation. o For example, it is unclear if the number 350 has two or three significant figures. We can avoid confusion by writing the number as 3.5×1023.5×102 to indicate two significant figures or as 3.50×1023.50×102 to indicate three. Exact Numbers Exact numbers have an unlimited number of significant figures. Exact numbers originate from three sources: Exact counting of discrete objects. For example, 10 pencils means 10.0000 . . . pencils and 3 atoms means 3.00000 . . . atoms. Defined quantities, such as the number of centimeters in 1 m. Because 100 cm is defined as 1 m then can be defined as: 100 cm=1 m means 100.00000... cm=1.0000000... m Note that some conversion factors (see Section 2.6) are defined quantities while others are not. Integral numbers that are part of an equation. For example, in the equation, Radius=diameter/2 The number 2 is exact and therefore has an unlimited number of significant figures.